Gyroscopic boat roll stabilizer with bearing cooling

ABSTRACT

A gyroscopic roll stabilizer includes an enclosure, a flywheel assembly, a bearing, a motor, and a bearing cooling circuit. The enclosure is mounted to a gimbal for rotation about a gimbal axis and configured to maintain a below-ambient pressure. The flywheel assembly includes a flywheel and flywheel shaft. The bearing rotatably mounts the flywheel assembly inside the enclosure for rotation about a flywheel axis. The bearing has an inner race and an outer race. The inner race is affixed to the flywheel shaft, and the outer race is held rotationally fixed relative to the enclosure. The motor is operative to rotate the flywheel assembly. The bearing cooling circuit is configured to transfer heat away from the bearing by recirculating cooling fluid along a closed fluid pathway. The gyroscopic roll stabilizer is configured to transfer heat away from the inner and/or outer race of the bearing to the cooling fluid.

This application claims the benefit of U.S. Provisional Application No.63/070,530, filed 26 Aug. 2020, and U.S. Provisional Application No.62/984,013, filed 2 Mar. 2020, the disclosures of which are incorporatedherein by reference in their entirety.

TECHNICAL FIELD

The present disclosure relates generally to boat roll stabilizers forreducing the sideways rolling motion of a boat and, more particularly,to controlled moment gyroscopes for reducing the roll of a boat based onthe gyroscopic effect.

BACKGROUND

The sideways rolling motion of a boat can create safety problems forpassengers and crew on boats, as well as cause discomfort to passengersnot accustomed to the rolling motion of the boat. A number oftechnologies currently exist to reduce the sideways rolling motion of aboat. One technology currently in use is active fin stabilization.Stabilizer fins are attached to the hull of the boat beneath thewaterline and generate lift to reduce the roll of the boat due to windor waves. In the case of active fin stabilization, the motion of theboat is sensed and the angle of the fin is controlled based on themotion of the boat to generate a force to counteract the roll. Finstabilization is most commonly used on large boats and is effective whenthe boat is underway. Fin stabilization technology is not usedfrequently in smaller boats and is generally not effective when the boatis at rest. Stabilizer fins also add to the drag of the hull and aresusceptible to damage.

Gyroscopic boat stabilization is another technology for roll suppressionthat is based on the gyroscopic effect. A control moment gyroscope (CMG)is mounted in the boat and generates a torque that can be used tocounteract the rolling motion of the boat. The CMG includes a flywheelthat spins at a high speed. A controller senses the attitude of the boatand uses the energy stored in the flywheel to “correct” the attitude ofthe boat by applying a torque to the hull counteracting the rollingmotion of the boat. CMGs work not only when a boat is underway, but alsowhen the boat is at rest. CMGs are also typically less expensive thanstabilizer fins, do not add to the drag of the hull, and are not exposedto risk of damage from external impacts.

Although, CMGs are gaining in popularity, particularly for smallerfishing boats and yachts, this technology has some limitations. Theenergy used to counteract the rolling motion of the boat comes from theangular momentum of the rotation of the flywheel at a high rate ofspeed. Consequently, heat builds up in the bearings supporting theflywheel and bearing failure can result if the operational temperatureof the bearings is exceeded. The flywheel is typically mounted inside anenclosure for safety reasons. In order to obtain the high spin rate, theflywheel is typically contained in a vacuum enclosure, which makes heatdissipation problematic.

Another problem with existing CMGs is that it takes a significant amountof time for the flywheel to “spin up,” i.e., to obtain its desiredoperating speed. In some CMGs currently on the market, it can take aslong as seventy minutes before the CMG is ready for use. The long “spinup” period means that the CMG cannot be used for trips of shortduration, which comprises a majority of boating occasions.

Thus, there remains a need for alternative approaches to gyroscopic boatstabilization, advantageously approaches that allow for better coolingof the bearings, so that performance can be improved.

SUMMARY

The present disclosure relates to a gyroscopic roll stabilizer for aboat. In an aspect, the gyroscopic roll stabilizer includes an enclosuremounted to a gimbal and configured to maintain a below-ambient pressure,a flywheel assembly including a flywheel and flywheel shaft, one or morebearings for rotatably mounting the flywheel assembly inside theenclosure, a motor for rotating the flywheel, and a bearing coolingsystem for cooling the bearings supporting the flywheel. In oneembodiment, the bearing cooling system comprises a heat sink that isdisposed within a cavity formed within the end of the flywheel shaft.Heat is transferred from the flywheel shaft to the heat sink and then bysolid and/or liquid conduction to the heat exchanger. In anotherembodiment, cooling is achieved by delivering a liquid coolant into atapered cavity in the end of the flywheel shaft. The cavity is shaped sothat the centrifugal force causes the liquid coolant to flow towards theopen end of the shaft, where the liquid coolant is collected by a fluidcollection system.

In another aspect, a gyroscopic roll stabilizer for a boat is disclosed.The gyroscopic stabilizer includes an enclosure, a flywheel assembly, afirst bearing, a bearing block, a motor, and a bearing cooling circuit.The enclosure is mounted to a gimbal for rotation about a gimbal axisand configured to maintain a below-ambient pressure. The flywheelassembly includes a flywheel and flywheel shaft. The first bearingrotatably mounts the flywheel assembly inside the enclosure for rotationabout a flywheel axis. The first bearing has an inner race and an outerrace, the inner race affixed to the flywheel shaft. The bearing block isdisposed between the outer race of the first bearing and the enclosureand configured to hold the outer race rotationally fixed relative to theenclosure. The motor is operative to rotate the flywheel assembly. Thebearing cooling circuit is configured to transfer heat away from theouter race of the first bearing. The bearing cooling circuit has aclosed fluid pathway for recirculating cooling fluid therein. The fluidpathway includes a fluid channel disposed between the bearing block andthe enclosure and having the cooling fluid therein. The gyroscopic rollstabilizer is configured to transfer heat away from the outer race ofthe first bearing to the bearing block, and from the bearing block tothe cooling fluid.

In another aspect, a method of operating a gyroscopic roll stabilizerfor a boat is disclosed. The method includes 1) maintaining a belowambient pressure within an enclosure surrounding a flywheel assembly,the flywheel assembly including a flywheel shaft and a spinningflywheel; 2) supporting the spinning flywheel for rotation about aflywheel axis via a bearing, the bearing comprising an inner race and anouter race, the inner race affixed to the flywheel shaft; 3) supportingthe outer race via a bearing block disposed between the outer race andthe enclosure and configured to hold the outer race rotationally fixedrelative to the enclosure; 4) dissipating heat from the outer race bytransferring the heat by conduction and convection to a cooling fluidflowing through a fluid channel disposed between the bearing block andthe enclosure; 5) cooling the cooling fluid by removing heat from thecooling fluid external to the portion of the enclosure maintained at thebelow-ambient pressure; and 6) recirculating the cooling fluid through aclosed fluid pathway that includes the fluid channel.

In another aspect, another gyroscopic roll stabilizer for a boat isdisclosed. The gyroscopic stabilizer includes an enclosure, a flywheelassembly, a first bearing, a motor, and a bearing cooling circuit. Theenclosure is mounted to a gimbal for rotation about a gimbal axis andconfigured to maintain a below-ambient pressure. The flywheel assemblyincludes a flywheel and flywheel shaft, with an open-ended cavity formedin an end of the flywheel shaft. The first bearing rotatably mounts theflywheel assembly inside the enclosure for rotation about a flywheelaxis. The first bearing has an inner race affixed to the flywheel shaftproximate the cavity and an outer race rotationally fixed relative tothe enclosure. The motor is operative to rotate the flywheel assembly. Aliquid heat transfer medium is disposed in the cavity. The bearingcooling circuit is configured to transfer heat away from the inner raceof the first bearing by recirculating a cooling fluid. The bearingcooling circuit includes a heat transfer shaft assembly and a closedfluid pathway. The heat transfer shaft assembly is rotationally fixedrelative to the flywheel axis and extends from the enclosure into thecavity so as to contact the liquid heat transfer medium. The closedfluid pathway for the cooling fluid extends through the heat transfershaft assembly to internally cool the heat transfer shaft assembly. Thegyroscopic roll stabilizer is configured to transfer heat away from theinner race of the first bearing to the flywheel shaft, and from theflywheel shaft to the liquid heat transfer medium, and from the liquidheat transfer medium to the heat transfer shaft assembly, and from theheat transfer shaft assembly to the cooling fluid.

In another aspect, a method of operating a gyroscopic roll stabilizerfor a boat is disclosed. The method includes 1) maintaining a belowambient pressure within an enclosure surrounding a flywheel assembly,the flywheel assembly including a flywheel shaft and a spinningflywheel; wherein the flywheel shaft has an open-ended cavity formed inan end of the flywheel shaft; wherein a liquid heat transfer medium isdisposed in the cavity; 2) supporting the spinning flywheel for rotationabout a flywheel axis via a bearing, the bearing comprising an innerrace and an outer race, the inner race affixed to the flywheel shaft; 3)dissipating heat from the inner race by transferring the heat byconduction and convection to a bearing cooling circuit configured totransfer heat by recirculating a cooling fluid along a closed fluidpathway; 4) cooling the cooling fluid by removing heat from the coolingfluid external to the portion of the enclosure maintained at thebelow-ambient pressure; and 5) recirculating the cooling fluid throughthe closed fluid pathway. The dissipating heat comprises internallycooling, by the cooling fluid, a heat transfer shaft assemblyrotationally fixed relative to the flywheel axis and extending from theenclosure into the cavity so as to contact the liquid heat transfermedium. In the method, heat is transferred away from the inner race ofthe bearing to the flywheel shaft, and from the flywheel shaft to theliquid heat transfer medium, and from the liquid heat transfer medium tothe heat transfer shaft assembly, and from the heat transfer shaftassembly to the cooling fluid.

The features, functions and advantages that have been discussed above,and/or are discussed below, can be achieved independently in variousaspects or may be combined in yet other aspects, further details ofwhich can be seen with reference to the following description and thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B illustrate a boat equipped with a CMG as hereindescribed.

FIG. 2 show an elevation view of a CMG configured as a boat rollstabilizer according to an embodiment.

FIG. 3 shows a section view through the enclosure of a CMG according toan embodiment.

FIG. 4 shows a partial section view of FIG. 3 .

FIG. 5 shows a cooling circuit for a CMG.

FIG. 6 shows a torque control system for the CMG.

FIG. 7 shows a partial section view illustrating the bearing coolingsystem according to another embodiment.

FIG. 8 shows a partial section view illustrating a CMG with both aninner race bearing cooling circuit and an outer race bearing coolingcircuit.

FIG. 9 shows a simplified schematic of a bearing cooling circuit forcooling the outer race.

FIG. 10 shows a simplified flowchart of an exemplary method for coolingthe outer race.

FIG. 11 shows a simplified schematic of a bearing cooling circuit forcooling the inner race.

FIG. 12 shows a simplified flowchart of an exemplary method for coolingthe inner race.

DETAILED DESCRIPTION

Referring now to the drawings, FIGS. 1A and 1B illustrate a controlmoment gyroscope (CMG) 10 mounted in a boat 5 for roll stabilization.Multiple embodiments of the CMG 10 are described. For convenience,similar reference numbers are used in the following description of theembodiments to indicate similar elements in each of the embodiments.

Referring now to FIGS. 2 and 3 , the main functional elements of the CMG10 comprise a single-axis gimbal 20, an enclosure 30 mounted to thegimbal 20 for rotation about a gimbal axis G, a flywheel assembly 40mounted by bearings 50 inside the enclosure, a motor 60 (FIG. 5 ) torotate the flywheel assembly 40, and a torque control system 70 (FIG. 5) to control precession of the flywheel assembly 40, with the energy ofthe flywheel assembly 40 transferred to the hull of the boat 5 tocounteract rolling motions. Each of the embodiments further comprises abearing cooling system 100 to cool the flywheel bearings 50. Variousdesigns of the bearing cooling system 100 are disclosed.

The gimbal 20 comprises a support frame 22 that is configured to besecurely mounted in the boat 5. Preferably, the gimbal 20 is mountedalong a longitudinal axis L of the boat 5 with the gimbal axis Gextending transverse to the longitudinal axis L. Conventionally, thegimbal 20 is mounted in the hull of the boat 5, but could be mounted atany location. The support frame 22 of the gimbal 20 comprises a base 24and two spaced-apart supports 26. A bearing 28 is mounted on eachsupport 26 for rotatably mounting the enclosure 30 to the supports 26.For this purpose, the enclosure 30 includes two gimbal shafts 32projecting from diametrically opposed sides of the enclosure 30. Thegimbal shafts 32 are rotatably journaled in the gimbal bearings 28 toallow the enclosure 30 (and flywheel assembly 40 disposed therein) torotate or precess about the gimbal axis G in the fore and aftdirections.

The basic elements of enclosure 30 are the same in the variousembodiments described herein but vary in some details depending on thedesign of the bearing cooling system 100. The enclosure 30 isadvantageously generally spherical in form and comprises two mainhousing sections 34 and two cover plates 36. The two main housingsections 34 join along a plane that typically bisects the sphericalenclosure 30. The cover plates 36 join the main housing sections 34along respective planes closer to the “poles” of the spherical enclosure30. All joints in the enclosure 30 are sealed to maintain abelow-ambient pressure within the enclosure 30 to reduce aerodynamicdrag on the flywheel assembly 40. Typical below-ambient pressures shouldbe in the range of 1-40 torr (133-5333 Pa, 0.02-0.77 psi). Although theconstruction of the enclosure 30 is generally the same in theembodiments herein described, the details of the housing sections 34 andcover plates 36 vary as described more fully below depending on thedesign of the bearing cooling system 100 used.

Referring to FIG. 3 , the flywheel assembly 40 conceptually comprises aflywheel 42 and flywheel shaft 44 that is mounted for rotation insidethe enclosure 30 of the gimbal 20 so that the axis of rotation F of theflywheel assembly 40 is perpendicular to the gimbal axis G. Thus, whenthe boat 5 is level such that gimbal axis G is horizontal, the axis ofrotation F of the flywheel shaft 44 will be in the vertical direction,typically perpendicular to the deck of the boat. The flywheel 42 andshaft 44 may be formed as a unitary piece, or may comprise two separatecomponents. In one exemplary embodiment, the diameter and the flywheel42 is approximately 20.5 inches; the flywheel assembly 40 has a totalweight of about 614 pounds; and the flywheel assembly 40 has a moment ofinertia of about 32,273 lbm in². When rotated at a rate of 9000 rpm, theangular momentum of the flywheel assembly 40 is about 211,225 lbm ft²/s.

The flywheel assembly 40 is supported by upper and lower bearingassemblies inside the enclosure 30. Each bearing assembly comprises abearing 50 mounted within a bearing block 58. Each bearing 50 comprisesan inner race 52 that is affixed to and rotates with the flywheel shaft44, an outer race 54 that is mounted inside the bearing block 58, andone or more ball bearings 56 disposed between the inner and outer races52, 54. The bearing blocks 58 are secured to the interior of theenclosure 30. Seals (not shown) may advantageously be disposed on thetop and bottom of the bearings 50 to contain lubricant in the bearings50.

The motor 60 rotates the flywheel assembly 40 at a high rate of speed(e.g., 9000 rpm). The motor 60 includes a rotor 62 that connects to theflywheel shaft 44 and a stator 64 that this secured to the enclosure 30by any suitable mounting system. Although the motor 60 is advantageouslymounted inside the enclosure 30, it is also possible to mount the motor60 on the exterior of the enclosure 30. In one embodiment, the motor 60operates on 230 Volt single phase AC power (or could be three-phase ACpower, or AC or DC battery power, such as from a lithium ion batterypack) and is able to accelerate a flywheel assembly with a moment ofinertia of about 32,273 lbm in² from rest to a rotational speed of 9000rpm preferably in about 30 minutes or less for an average accelerationof about 5 rpm/s, and more preferably in about 20 minutes or less for anaverage acceleration of about 7.75 rpm/s, and even more preferably inabout 10 minutes or less for an average acceleration of about 15 rpm/s(or 1.57 radians/s²).

The torque control system 70, shown in FIG. 5 , controls the rate ofprecession of the flywheel assembly 40 about the gimbal axis G. Therolling motion of a boat 5 caused by wave action can be characterized bya roll angle and roll rate. The rolling motion causes the flywheel 42 toprecess about the gimbal axis G. Sensors 74, 76 measure the roll angleand roll rate respectively, which are fed to a controller 72. Thecontroller 72 generates control signals to control an active brakingsystem or other torque applying device 78 that controls the rate ofprecession of the flywheel assembly 40. By controlling the rate ofprecession, the flywheel assembly 40 generates a torque in opposition tothe rolling motion. This torque is transferred through the gimbal 20 tothe boat 5 to dampen the roll of the boat 5. An example of the activebraking system 78 is described in U.S. Patent Application PublicationNo. US20200317308.

When the flywheel assembly 40 rotates at high speed, the bearings 50 andmotor 60 will generate a substantial amount of heat, which could lead tobearing and/or motor failure. Conventional air and liquid coolingtechniques are not suitable for bearings 50 or other heat generatingcomponents contained within a vacuum or significantly below ambientpressure environment. Various embodiments of the bearing cooling system100 are disclosed herein allow cooling of bearings 50 and optionallyother heat generating components contained within the enclosure 30without direct contact of the recirculated liquid coolant with thebearings 50 or other moving heat generating components, which wouldresult in high frictional losses. In general, heat is transferred bysolid and/or liquid conduction to a heat sink that is cooled by oil,glycol, or other liquid coolant. Liquid cooling enables more heat to bedissipated compared to air cooling or gaseous convection and conduction.Reliance on gaseous convection and conduction in existing CMGs imposeslimitations on the amount of heat that can be dissipated because theinterior of the enclosure 30 is typically maintained at a below ambientpressure. The limited heat transfer capacity in conventional CMGsimposes limitations on the size of the electric motor that is used,which in turn extends the time required to engage and use theconventional CMG. Because the electric motor in conventional CMGs isundersized to avoid heat generation, conventional CMGs requiresignificant time to accelerate the flywheel assembly 40 to a speed thatprovides the desired counter-torque and roll stabilization. Providingmore efficient cooling of the bearings 50 as herein described enablesuse of a larger and more powerful motor 60 and faster acceleration ofthe flywheel assembly 40 so that the benefits of using the CMG 10 can beobtained in significantly shorter time periods.

FIG. 6 is a schematic diagram of a cooling circuit 80 for circulatingthe liquid coolant. A fluid reservoir 82 contains the liquid coolantwhich is circulated in a “closed” circuit by a fluid pump 84. The fluidreservoir 82 may include a heat exchanger 83 to cool the liquid coolantin the fluid reservoir 82. After leaving the fluid reservoir 82, theliquid coolant passes through the heat exchanger 86 where it adsorbs andcarries away heat generated by the bearings 50, as described more fullybelow. In some embodiments, heat is transferred from the flywheel shaft44 to a heat sink and then by solid and liquid conduction to the heatexchanger 86. In other embodiments, heat is transferred from theflywheel shaft 44 to the liquid coolant which is circulated through acavity 46 in the flywheel shaft 44. Accordingly, the heat transfer tothe liquid coolant occurs within the cavity 46 of the flywheel shaft 44so the heat exchanger 86 is not required. In some embodiments, ascavenging circuit 88 is provided to collect liquid coolant that mayseep into the interior of the enclosure 30 and return the liquid coolantto the fluid reservoir 82.

FIG. 4 illustrates one embodiment of a bearing cooling system 100 usinga heat sink to dissipate heat generated by the bearings 50 and/or motor60. While the present discussion of the bearing cooling system 100 isgenerally in the context of cooling the upper bearing 50, it should benoted that the upper and lower bearings 50 may be cooled in similarways, if desired. For the upper bearing 50, the upper portion of theflywheel shaft 44 is secured within bearing 50 that is, in turn, securedwithin the enclosure 30. Each bearing 50 includes an outer race 54, oneor more ball bearings 56, and an inner race 52 that engages the flywheelshaft 44 and rotates therewith. The flywheel shaft 44 includes a cavity46 at each end thereof. The cavity 46 in each end of the flywheel shaft44 is open at one end and includes a side wall and a bottom wall(opposite the opening of the cavity 46).

A heat transfer member 102 that functions as a heat sink is suspended inthe cavity 46. The heat transfer member 102 does not directly engage theside or bottom walls of the cavity 46. Rather, the outer surface of theheat transfer member 102 is spaced from the side and bottom walls of thecavity 46. In one embodiment, the spacing between the heat transfermember 102 and the walls of the cavity 46 is approximately 0.035-0.095inches. Various materials can be used for the heat transfer member 102discussed herein. Preferably, copper, aluminum, or alloys thereof areused because of their relatively high thermal conductivity.

A heat transfer medium is contained in the gap between the heat transfermember 102 and the walls of the cavity 46. As one example, the heattransfer medium comprises a low vapor pressure fluid that is suitablefor the low pressure environment in the enclosure 30. A low vaporpressure fluid is a liquid, such as oil, that has a relatively lowboiling point compared to water and is suitable for employment in avacuum environment. For example, aerospace lubricants, such asperfluoropolyether (PFPE) lubricants, designed for vacuum environmentscan be used as the heat transfer medium. The low vapor pressure fluidenables transfer of heat from the flywheel shaft 44 to the heat transfermember 102 by liquid conduction and liquid convection. A labyrinth seal110 extends around the heat transfer member 102 and effectively sealsthe cavity 46 such that the heat transfer medium is maintained withinthe cavity 46. The labyrinth seal 110 is preferably fixed to the heattransfer member 102, which means that the flywheel shaft 44 rotatesaround the labyrinth seal 110.

As seen in FIG. 4 , heat transfer member 102 extends from cavity 46,through an opening in a cover plate 36 forming a part of the enclosure30, and into a heat exchanger 86. Seals 108 located in correspondinggrooves in the cover plate 36 maintain vacuum within the enclosure 30.The heat exchanger 86 is mounted to the exterior surface of the coverplate 36. The heat exchanger 86 comprises a housing 106 and a heatexchange plate 104 confined within the housing 106. The heat transfermember 102 is secured by a fastener 103 to the heat exchange plate 104so that the heat transfer member 102 is effectively suspended in thecavity 46 formed in the flywheel shaft 44. More particularly, the heatexchange plate 104 includes a recess in the bottom surface thereof thatreceives the end of the of the heat transfer member 102. The surfacecontact between the end of the heat transfer member 102 and the heatexchange plate 104 facilitates the efficient transfer of heat by solidconduction from the heat transfer member 102 to the heat exchange plate104.

A liquid coolant, such as a glycol coolant, is circulated through theheat exchanger 86 to absorb and carry heat away from the heat exchangeplate 104. The upper surface of the heat exchange plate 104 can beprovided with fluid channels and/or cooling fins to increase the surfacearea of the heat exchange plate 104 and to facilitate heat transfer fromthe heat exchange plate 104 to the liquid coolant.

Heat is generated in the inner and outer races of the bearing assemblies50 due to the high side loads generated from the CMG's torque as theenclosure 30 rotates about the gimbal axis G. The outer race 54 has acontinuous heat conductive path through the enclosure 30 which permitsthe heat associated with the outer race 54 to be conveyed into theatmosphere. The inner race 52 requires a heat sink path through parts ofthe enclosure 30. In this embodiment, heat from the inner race 52 of thebearing assembly 50 is transferred by solid conduction to the flywheelshaft 44. The heat is then transferred by liquid conduction from theflywheel shaft 44 to the heat transfer member 102, and by solidconduction through the heat transfer member 102 to the heat exchangeplate 104 that continuously conveys the heat into surrounding liquidcoolant. In some embodiments, the heat exchanger 86 could employ air orgas cooling rather than liquid cooling.

FIG. 7 illustrates an alternate bearing cooling system 100 that alsouses a heat sink. This bearing cooling system 100 in FIG. 7 is similarto the design shown in FIG. 4 . The main differences lie in the shapesof the heat transfer member 102, labyrinth seal 110, and the heatexchange plate 104. In this embodiment, the heat transfer member 102includes a channel that increases the surface area exposed to the heattransfer medium. The heat exchange plate 104, in contrast to theprevious embodiment, has a smooth top surface without grooves or vanes.The heat transfer path, however, is conceptually similar. That is, heatassociated with the inner race 52 is transferred to the flywheel shaft44 by solid conduction. The cavity 46 formed in the flywheel shaft 44,like the above design (FIG. 4 ), is configured to hold the heat transfermedium (typically a low vapor pressure fluid) so that heat istransferred by liquid conduction from the flywheel shaft 44 through theheat transfer medium to the lower portion of a heat transfer member 102.Thereafter, heat in the heat transfer member 102 is transferred by solidconduction to the heat exchange plate 104. A liquid coolant iscirculated through the heat exchanger 86. In doing so, the liquidcoolant contacts the heat exchange plate 104 and heat associated withthe heat exchange plate 104 is transferred to the circulating liquidcoolant.

FIG. 8 is another alternative design for a bearing cooling system 100for a gyroscopic boat stabilizer (e.g., CMG 10). This design is similarin concept to the preceding designs but differs in a number of respects.For example, the bearing cooling system 100 of FIG. 8 has an optionalbearing cooling circuit 100′ (see FIG. 9 ) for the outer race 54 of thebearing. As another example, the bearing cooling system 100 of FIG. 8has a heat transfer shaft assembly 130 that extends into the cavity 46of the flywheel shaft 44, and that is internally cooled. Except wherenoted below, the basic design of the gimbal 20, enclosure 30, flywheelassembly 40, bearing assemblies 50 and motor 60 (FIG. 5 ) of the CMG 10shown in FIG. 8 are essentially the same as previously described.Therefore, the following description will not reiterate the details ofthese elements.

Referring to FIG. 8 , the CMG 10 includes an enclosure 30, a flywheelassembly 40, a bearing 50, a bearing block 58, a motor 60, and a bearingcooling circuit. The portions of the enclosure 30, flywheel assembly 40,and motor 60 (not shown in FIG. 8 ) are similar to that discussed above,and only briefly discussed herein for clarity. As discussed above, theenclosure 30 is mounted to the gimbal 20 for rotation about the gimbalaxis G, and is configured to maintain a below-ambient pressure insidethe enclosure 30. The flywheel assembly 40 is rotatably mounted in theenclosure 30, and includes flywheel 42 and flywheel shaft 44. Theflywheel assembly 40 is rotatably mounted inside the enclosure 30 forrotation about flywheel axis F. While the flywheel assembly 40 isadvantageously rotatably mounted in the enclosure 30 by at least twobearings 50 disposed towards opposing “poles” of the flywheel assembly40, in some versions the flywheel assembly 40 is rotatably mounted byone bearing 50. The cooling of the upper bearing 50 (typically locatedgenerally opposite the motor 60) will be discussed, it being understoodthat other bearings 50, if present, are advantageously cooled by similarcorresponding bearing cooling circuits, or sub-portions of a bearingcooling circuit.

As is conventional, the bearing includes inner race 52 and outer race54. The inner race 52 is affixed to the flywheel shaft 44 so that theinner race 52 rotates with the flywheel shaft 44. The outer race 54 ismounted to a bearing block 58, and the bearing block 58 is mounted tothe enclosure 30, so that the outer race 54 is rotationally fixedrelative to the enclosure 30. The mounting of the bearing block 58 tothe enclosure 30 may be via any suitable means, such as by suitablelip(s) in the bearing block 58 and one or more bearing cap plates 59 aheld by screws. Likewise, the affixing of the inner race 52 to theflywheel shaft 44 may be by any suitable means, such as press fitting,and/or suitable lip(s) in the flywheel shaft 44 and one or more bearingcap plates 59 b held by screws. The bearing block 58 may be generallyround in cross-section (perpendicular to flywheel axis F), but this isnot required and any suitable shape may be employed, including facetedshapes.

A bearing cooling circuit 100′ is used to transfer heat away from theouter race 54. See FIG. 9 . The bearing cooling circuit 100′ includes afluid pathway 210 that is closed, and is sometimes referred to as theclosed fluid pathway 210. The fluid pathway 210 is used forrecirculating cooling fluid 90, with the cooling fluid 90 being used aspart of the heat dissipation mechanism for removing heat from the outerrace 54. The cooling fluid 90 may be any suitable fluid, with a liquidsuch as glycol and/or glycol mixtures being particular examples. Thefluid pathway 210 includes a fluid channel 220 disposed near the outerrace 54 and between the bearing block 58 and the enclosure 30. The fluidchannel 220 has cooling fluid 90 therein. The fluid channel 220 isadvantageously jointly defined by the bearing block 58 and the enclosure30. For example, the bearing block 58 may include one or more grooves222 on its outer surface. Such groove(s) 222 are conceptually closedoff, to form the fluid channel 220, by the inner wall of enclosure 30facing the bearing block 58. Alternatively and/or additionally, theenclosure 30 may include one or more grooves 222 on an inner surfacethat faces the bearing block 58. Such groove(s) 222 are conceptuallyclosed off, to form the fluid channel 220, by the outer surface of thebearing block 58 facing the enclosure 30. Note that the groove(s) 222may be oriented perpendicular to the flywheel axis F, or mayadvantageously spiral around the flywheel axis F, such as by beinghelical or other spiral shape. Alternatively, the groove(s) 222 may windaround the interface of the bearing block 58 and the enclosure 30 in anysuitable fashion, such as in a sinusoidal shape, or a zig-zag shape,whether regular or irregular. Optionally, the fluid pathway 210peripherally surrounds the flywheel axis F, such as by circumnavigatingthe bearing block 58. The flow direction in the fluid pathway 210 may bein any suitable direction, such as clockwise or counter-clockwise, orboth as appropriate. When the fluid channel 220 is spiral (e.g.,helical), the cooling fluid 90 advantageously flows through the fluidchannel 220 spirally (e.g., helically) either outward away from theflywheel 42, or inward toward flywheel 42.

The bearing cooling circuit 100′ optionally also includes a reservoir 82for the cooling fluid 90 flowing through the cooling circuit 100′, and afluid pump 84 operative to recirculate the cooling fluid 90 throughbearing cooling circuit 100′. Thus, the fluid pathway 210 for thecooling fluid 90 optionally extends through the fluid reservoir 82, thefluid channel 220, and the fluid pump 84. Thus, the pump 84 isoperatively connected to the fluid channel 220 and configured torecirculate the cooling fluid 90 through the fluid channel 220 to removeheat from the outer race 54 via the bearing block 58. The presence ofthe bearing cooling circuit 100′ in the gyroscopic roll stabilizerallows the gyroscopic roll stabilizer to be configured to transfer heataway from the outer race 54 to the bearing block 58, and from thebearing block 58 to the cooling fluid 90. Note that a heat exchanger,such as heat exchanger 83, is operatively connected to closed fluidpathway 210 and configured to remove heat from the cooling fluid 90 toambient after the cooling fluid 90 has passed through the fluid channel220.

In some aspects, the fluid pathway 210 also includes an inlet port 206and an outlet port 208. The inlet port 206 is operatively disposedbetween the pump 84 and the fluid channel 220, and operative to allowpassage of the cooling fluid 90 into the enclosure 30 toward the fluidchannel 220. The outlet port 208 is operatively disposed between thefluid channel 220 and the heat exchanger 83, and operative to allowpassage of the cooling fluid 90 out of the enclosure 30 toward the heatexchanger 83.

For the FIG. 8 arrangement, the heat flow for dissipating heat from theouter race 54 is from the outer race 54, to the bearing block 58, thento the cooling fluid 90 in the fluid channel 220, then to external tothe CMG 10 via the heat exchanger 83. Note that the heat is transferredby solid conduction from the outer race 54 to the bearing block 58, thenby solid conduction through the bearing block 58, then by conduction andconvection to the cooling fluid 90.

A method (300) of operating a gyroscopic roll stabilizer 10 thatincludes a bearing cooling circuit 100′ for the outer race 54 of thebearing discussed above is shown in FIG. 10 . The method (300) includesmaintaining (310) a below ambient pressure within enclosure 30, withenclosure 30 surrounding flywheel assembly 40. The flywheel assembly 40includes flywheel shaft 44 and spinning flywheel 42. The method alsoincludes supporting (320) the spinning flywheel for rotation aboutflywheel axis F via bearing 50, the bearing 50 comprising inner race 52and outer race 54, with the inner race 52 affixed to the flywheel shaft44. The method further includes supporting (330) the outer race 54 viabearing block 58 disposed between the outer race 54 and the enclosure 30and configured to hold the outer race 54 rotationally fixed relative tothe enclosure 30. The method also includes dissipating (340) heat fromthe outer race 54 by transferring the heat by conduction and convectionto a cooling fluid 90 flowing through fluid channel 220 disposed betweenbearing block 58 and enclosure 30. Further, the method includes cooling(360) the cooling fluid 90 by removing heat from the cooling fluid 90external to the portion of the enclosure 30 maintained at thebelow-ambient pressure. In addition, the method includes recirculating(370) the cooling fluid 90 through closed fluid pathway 210 thatincludes the fluid channel 220. Note that the recirculating (370)optionally includes routing (372) the cooling fluid 90 from the fluidchannel 220 to reservoir 82, and pumping (374) the cooling fluid 90 fromthe reservoir 82 to the fluid channel 220, and the cooling (360) thecooling fluid 90 comprises cooling the cooling fluid 90 via a heatexchanger 83 disposed external to the enclosure 30. Optionally, theoperating method includes driving (350) the flywheel 42 to spin aboutflywheel axis F via motor 60 disposed internal to the enclosure 30. Notethat the various steps of method (300) may be carried out in anysuitable order, including in whole or in part in parallel. For example,at least the maintaining (310), the supporting (320) the flywheel, thesupporting (330) the outer race, and the dissipating (340) areadvantageously carried out simultaneously.

Referring again to FIG. 8 , the CMG 10 alternatively and/or additionallyincludes an arrangement for dissipating heat from the inner race 52. Inthis regard, the flywheel shaft 44 includes open-ended cavity 46 formedin an end of the flywheel shaft 44. A liquid heat transfer medium 122 isdisposed in cavity 46. The liquid heat transfer medium 122 may be anysuitable material for operating in the low-pressure environment of theenclosure 30. For example, the liquid heat transfer medium 122 may behydrocarbon oils (alkylated aromatics as well as alkanes, paraffinicmineral oils, and other synthetic hydrocarbons), fluorocarbon oils (suchas PFPE), silicone fluids of various chain lengths (e.g.,polydimethylsiloxane (PDMS)), glycol mixtures, and combinations thereof.The liquid heat transfer medium 122 is held in cavity 46 by one or moresuitable seals 125. Note that the inner race 52 is affixed to theflywheel shaft 44 proximate cavity 46.

A bearing cooling circuit 100″ is configured to transfer heat away fromthe inner race 52 of the by recirculating cooling fluid 90. See FIG. 11. As with bearing cooling circuit 100′, the cooling fluid 90 in bearingcooling circuit 100″ may be any suitable fluid, with a liquid such asglycol and/or glycol mixtures being particular examples. Bearing coolingcircuit 100″ includes a heat transfer shaft assembly 130 rotationallyfixed relative to the flywheel axis F and extending from the enclosure30 into cavity 46 so as to contact liquid heat transfer medium 122. Thebearing cooling circuit 100″ also includes a closed fluid pathway 210for the cooling fluid 90 that extends through the heat transfer shaftassembly 130 to internally cool the heat transfer shaft assembly 130.The CMG 10 is configured to transfer heat away from the inner race 52 tothe flywheel shaft 44, and from the flywheel shaft 44 to the liquid heattransfer medium 122, and from the liquid heat transfer medium 122 to theheat transfer shaft assembly 130, and from the heat transfer shaftassembly 130 to the cooling fluid 90. Note that the cavity 46 is wider(in the horizontal direction of FIG. 8 ) than the corresponding sectionof the heat transfer shaft assembly 130. Thus, the heat transferassembly 130 and the inner wall of the cavity 46, assuming both areround in cross-section, are annularly spaced from one another by a gap,and the liquid heat transfer medium 122 is disposed in this gap. Optimalsizing of this gap may depend on the viscosity, heat transfer, and othercharacteristics of the heat transfer medium 122, which impact theviscous drag and/or corresponding heat generation of the heat transfermedium 122. In some aspects, this gap is advantageously in the range ofabout one half to one and a half inches.

In some aspects, the heat transfer shaft assembly 130 is a simpleunified shaft that includes an internal chamber for the cooling fluid tobe circulated through. In other aspects, the heat transfer shaftassembly 130 includes a shaft 131, a sleeve 136, and fluid channel 120.The shaft 131 extends from the enclosure 30 and into cavity 46. Theshaft 131 advantageously has outer groove(s) 132 and an inner passage134. As with groove(s) 222, groove(s) 132 may be oriented perpendicularto the flywheel axis F, or may advantageously spiral around the flywheelaxis F, such as by being helical or other spiral shape. Alternatively,groove(s) 132 may wind around the shaft 131 in any suitable fashion,such as in a sinusoidal shape, or a zig-zag shape, whether regular orirregular. Advantageously, the groove(s) 132 peripherally surround theflywheel axis F, such as by circumnavigating the shaft 131. The sleeve136 is disposed about the shaft 131 in spaced relation to the “floor” ofthe groove(s) 132 and in spaced relation to an inner wall on flywheelshaft 44 defining the cavity 46. A fluid channel 120 is jointly definedby the sleeve 136 and the groove(s) 132, with the fluid channel 120having the cooling fluid 90 therein. The closed fluid pathway 210extends through fluid channel 120.

Note that in alternative embodiments, the groove(s) 132 arealternatively and/or additionally formed on the sleeve 136. Thus, itshould be considered that the fluid channel 120 is jointly formed by theshaft 131 and sleeve 136, regardless of whether the groove(s) 132 are inthe shaft 131, or the sleeve 136, or both.

In some aspects, the bearing cooling circuit 100″ further includes apump 84 and a heat exchanger 83. The pump 84 is operatively connected tothe fluid channel 120 and configured to recirculate the cooling fluid 90through the fluid channel 120 to remove heat from the inner race 52 viathe flywheel shaft 44, the liquid heat transfer medium 122, and heattransfer shaft assembly 130. The heat exchanger 83 is operativelyconnected to the closed fluid pathway 210 and configured to remove heatfrom the cooling fluid 90 to ambient after the cooling fluid 90 haspassed through fluid channel 120.

Cooling fluid 90 flows through the bearing cooling circuit 100″,including the fluid channel 120. When shaft 131 with inner passage 134is present, the inner passage 134 may be downstream relative to thefluid channel 120 along the fluid pathway 210, so that cooling fluid 90flows through the fluid channel 120, and then out of the heat transfershaft assembly 130 via the inner passage 134. In other aspects, the flowis reversed so that cooling fluid 90 flows through the inner passage134, and then out of the heat transfer shaft assembly 130 via the fluidchannel 120.

For the FIG. 8 arrangement, the heat flow for dissipating heat from theinner race 52 is from the inner race 52, to the flywheel shaft 44, thento the liquid heat transfer medium 122, then to the heat transfer shaftassembly 130, then to the cooling fluid 90, typically then to externalto the CMG 10 via the heat exchanger 83. Note that the heat istransferred by solid conduction from the inner race 52 to the flywheelshaft 44, then by conduction and convection to the liquid heat transfermedium 122, then by conduction and convection to the heat transfer shaftassembly 130, then by conduction and convection to the cooling fluid 90.

A method (400) of operating a gyroscopic roll stabilizer that includes abearing cooling circuit 100″ for the outer race 54 of the bearingdiscussed above is shown in FIG. 12 . The method (400) includesmaintaining (410) a below ambient pressure within enclosure 30, with theenclosure 30 surrounding flywheel assembly 40. The flywheel assembly 40includes a flywheel shaft 44 and a spinning flywheel 42. The flywheelshaft 44 has an open-ended cavity 46 formed in an end of the flywheelshaft 44. A liquid heat transfer medium 122 is disposed in the cavity46. The method also includes supporting (420) the spinning flywheel forrotation about flywheel axis F via bearing 50, the bearing 50 havinginner race 52 and outer race 54, with the inner race 52 affixed to theflywheel shaft 44. The method further includes dissipating (440) heatfrom the inner race 52 by transferring the heat by conduction andconvection to bearing cooling circuit 100″ configured to transfer heatby recirculating cooling fluid 90 along closed fluid pathway 210. Thedissipating heat comprises internally cooling, by the cooling fluid 90,heat transfer shaft assembly 130 rotationally fixed relative to theflywheel axis and extending from the enclosure 30 into the cavity 46 soas to contact the liquid heat transfer medium 122. In some aspects, theheat transfer shaft assembly 130 includes a shaft 131 and a sleeve 136,as described above, with the fluid channel 120, and the closed fluidpathway 210 extends through the fluid channel 120. Further, the methodincludes cooling (460) the cooling fluid 90 by removing heat from thecooling fluid 90 external to the portion of the enclosure 30 maintainedat the below-ambient pressure. In addition, the method includesrecirculating (470) the cooling fluid 90 through closed fluid pathway210. Note that the recirculating (470) optionally includes routing (472)the cooling fluid 90 from the heat transfer shaft assembly 130 toreservoir 82, and pumping (474) the cooling fluid 90 from the reservoir82 to the heat transfer shaft assembly 130, and the cooling (460) thecooling fluid 90 comprises cooling the cooling fluid 90 via a heatexchanger 83 disposed external to the enclosure 30. Optionally, theoperating method includes driving (450) the flywheel 42 to spin aboutflywheel axis F via motor 60 disposed internal to the enclosure 30. Inthe method, heat is transferred away from the inner race 52 of bearingto the flywheel shaft 44, and from the flywheel shaft 44 to the liquidheat transfer medium 122, and from the liquid heat transfer medium 122to the heat transfer shaft assembly 130, and from the heat transfershaft assembly 130 to the cooling fluid 90. Note that the various stepsof method (400) may be carried out in any suitable order, including inwhole or in part in parallel. For example, at least the maintaining(410), the supporting (420) the flywheel, and the dissipating (440) areadvantageously carried out simultaneously.

Note that the discussion above has generally been in the context of agiven end of the flywheel assembly 40 being rotationally supported inthe enclosure 30 by a single bearing 50. However, it should be notedthat one or both ends (e.g., just north end, just south end, or bothnorth and south ends) of the flywheel shaft 42 may alternatively besupported by a corresponding plurality of bearings 50, such as two ormore stacked bearings 50 at one or both ends.

Further note that while not required, the CMG 10 advantageously includesboth bearing cooling circuit 100′ and bearing cooling circuit 100″(instead of just one or the other) so that heat is efficientlytransferred away from both the inner race 52 and the outer race 54. Insome embodiments, bearing cooling circuit 100′ and bearing coolingcircuit 100″ share a common reservoir 82 and heat exchanger 84 (andoptionally inlet port 206, and outlet port 208), so as to form ameta-circuit that shares cooling fluid 90 between fluid channel 220 andthe heat transfer shaft assembly 130. For example, the fluid channel 220and the heat transfer shaft assembly 130 may be disposed along a commonbearing cooling circuit 100, such that the fluid channel 220 is disposedin series with and downstream/upstream of the heat transfer shaftassembly 130 (and fluid channel 120), before/after the common reservoir82, in a bearing cooling circuit 100 that cools both the inner race 52and the outer race 54.

The bearing cooling systems 100 (which may be alternatively denoted 100′or 100″) as herein described allow much greater heat dissipationcompared to current technology, which enables use of a larger motor 60,and advantageously lower operating temperature even with the largermotor 60. The larger motor and lower operating temperature enable rapidspin up and spin down of the flywheel assembly 40, and a significantlylower time to engage as discussed further below.

In use, the gimbal 20 is normally locked during spin up, i.e., while theflywheel assembly 40 is being accelerated, to prevent precession of theflywheel 42 until a predetermined rotational speed is achieved. The CMG10 can be locked to prevent rotation of the enclosure 30 by the activebraking system 78. When the CMG 10 is unlocked, precession of theflywheel 42 will place side loads on the bearings 50. The bearingfriction from the side loading of the bearings 50 generates heat. Inaddition, the bearing friction from the side loading also adds drag,which must be overcome by the motor 60 in order to continue accelerationof the flywheel's rotation. Thus, the frictional losses of side loadingthe bearings 50 have two impacts: generating heat and increasing theload on the motor 60.

Conceptually, there are two main sources of heat in a CMG: heatgenerated by the motor inside the enclosure 30 and heat generated bybearing friction. A large percentage of the heat budget is needed todissipate heat from the bearings in order to prevent bearing failure.The remaining portion of the heat budget, after accounting for bearingcooling, determines the size of the motor that can be used inside theenclosure.

The bearing cooling systems 100 as described herein enable moreefficient heat transfer, which enables a far greater heat transfercapacity and an increased heat budget. The increased heat budget meansthat larger and more powerful motors 60 that generate more heat can beused without causing bearing failure. With a larger and more powerfulmotor 60, the improved CMG 10 of the present disclosure is able toachieve greater acceleration of the flywheel assembly 40 and lower timeto engage than a conventional CMG. In addition to the higher rates ofacceleration, which naturally lead to lower times to engage assuming thesame minimum operating speed, a larger motor 60 enables the flywheelassembly 40 to be engaged at a lower operating speed (e.g., a lowerpercentage of nominal operating speed), which further reduces the timeto engage, because the larger motor 60 is able to overcome theadditional friction from the loading of the bearings 50. In someembodiments, the motor 60 is configured to enable the CMG 10 to beunlocked in under twenty minutes, and preferably in under ten minutesand more preferably in under five minutes. By combining higheracceleration with lower operating speeds at the time of engagement, atime to engage can be reduced to a few minutes. The rapid spin up andshorter time to engage enables beneficial use of the CMG 10 even forshort trip times, which makes up a majority of boating trips. Thus, therapid spin-up enables the CMG 10 to be used on a greater number ofboating occasions.

The disclosure of U.S. Patent Application Publication No. US20200317308is incorporated herein by reference in its entirety.

The present disclosure may, of course, be carried out in other ways thanthose specifically set forth herein without departing from essentialcharacteristics of the disclosure. The present embodiments are to beconsidered in all respects as illustrative and not restrictive, and allchanges coming within the meaning and equivalency range of the appendedclaims are intended to be embraced therein.

What is claimed is:
 1. A gyroscopic roll stabilizer for a boat, thegyroscopic roll stabilizer comprising: an enclosure mounted to a gimbalfor rotation about a gimbal axis and configured to maintain abelow-ambient pressure; a flywheel assembly including a flywheel andflywheel shaft, with a cavity that is open-ended formed in an end of theflywheel shaft; a first bearing for rotatably mounting the flywheelassembly inside the enclosure for rotation about a flywheel axis; thefirst bearing comprising an inner race affixed to the flywheel shaftproximate the cavity and an outer race rotationally fixed relative tothe enclosure; a motor operative to rotate the flywheel assembly; aliquid heat transfer medium disposed in the cavity; a bearing coolingcircuit configured to transfer heat away from the inner race of thefirst bearing by recirculating a cooling fluid; the bearing coolingcircuit comprising: a heat transfer shaft assembly rotationally fixedrelative to the flywheel axis and extending from the enclosure into thecavity so as to contact the liquid heat transfer medium; a closed fluidpathway for the cooling fluid that extends through the heat transfershaft assembly to internally cool the heat transfer shaft assembly;wherein the closed fluid pathway extends into the cavity inside the heattransfer shaft assembly; wherein the gyroscopic roll stabilizer isconfigured to transfer heat away from the inner race of the firstbearing to the flywheel shaft, and from the flywheel shaft to the liquidheat transfer medium, and from the liquid heat transfer medium to theheat transfer shaft assembly, and from the heat transfer shaft assemblyto the cooling fluid.
 2. The gyroscopic roll stabilizer of claim 1,wherein the heat transfer shaft assembly comprises: a shaft extendingfrom the enclosure and into the cavity; the shaft having an outer grooveand an inner passage; a sleeve disposed about the shaft in spacedrelation to the groove and in spaced relation to an inner wall definingthe cavity; a fluid channel jointly formed by the sleeve and the groove,the fluid channel having the cooling fluid therein; wherein the closedfluid pathway extends through the fluid channel.
 3. The gyroscopic rollstabilizer of claim 2, wherein the bearing cooling circuit furthercomprises: a fluid pump operatively connected to the fluid channel andconfigured to recirculate the cooling fluid through the fluid channel toremove heat from the inner race via the flywheel shaft, the liquid heattransfer medium, and the sleeve; a heat exchanger operatively connectedto the closed fluid pathway and configured to remove heat from thecooling fluid to ambient after the cooling fluid has passed through thefluid channel.
 4. The gyroscopic roll stabilizer of claim 2, wherein theinner passage is downstream relative to the fluid channel along theclosed fluid pathway.
 5. The gyroscopic roll stabilizer of claim 2,wherein the groove is spiral.
 6. The gyroscopic roll stabilizer of claim5, wherein the groove is helical.
 7. The gyroscopic roll stabilizer ofclaim 2: further comprising a bearing block disposed between the outerrace of the first bearing and the enclosure and configured to hold theouter race rotationally fixed relative to the enclosure; wherein thebearing cooling circuit further comprises another fluid channel disposedbetween the bearing block and the enclosure and having the cooling fluidtherein; wherein the another fluid channel is downstream of the heattransfer shaft assembly; wherein the gyroscopic roll stabilizer isconfigured to transfer heat away from the outer race of the firstbearing to the bearing block, and from the bearing block to the coolingfluid.
 8. The gyroscopic roll stabilizer of claim 1, wherein the coolingfluid comprises glycol.
 9. The gyroscopic roll stabilizer of claim 1,wherein the liquid heat transfer medium comprises a hydrocarbon oil. 10.The gyroscopic roll stabilizer of claim 1, wherein the gyroscopic rollstabilizer is configured such that heat is transferred from the innerrace to the cooling fluid via: solid conduction from the inner race tothe flywheel shaft; liquid conduction and convection from the flywheelshaft to the heat transfer shaft assembly via the liquid heat transfermedium; liquid conduction and convection from the heat transfer shaftassembly to the cooling fluid.
 11. A method of operating a gyroscopicroll stabilizer for a boat, the method comprising: maintaining a belowambient pressure within an enclosure surrounding a flywheel assembly,the flywheel assembly including a flywheel shaft and a spinningflywheel; wherein the flywheel shaft has a cavity that is open-endedformed in an end of the flywheel shaft; wherein a liquid heat transfermedium is disposed in the cavity; supporting the spinning flywheel forrotation about a flywheel axis via a bearing, the bearing comprising aninner race and an outer race, the inner race affixed to the flywheelshaft; dissipating heat from the inner race by transferring the heat byconduction and convection to a bearing cooling circuit configured totransfer heat by recirculating a cooling fluid along a closed fluidpathway; cooling the cooling fluid by removing heat from the coolingfluid external to a portion of the enclosure maintained at thebelow-ambient pressure; and recirculating the cooling fluid through theclosed fluid pathway; wherein the dissipating heat comprises internallycooling, by the cooling fluid, a heat transfer shaft assemblyrotationally fixed relative to the flywheel axis and extending from theenclosure into the cavity so as to contact the liquid heat transfermedium by routing the cooling fluid through the heat transfer shaftassembly disposed in the cavity; wherein the closed fluid pathwayextends into the cavity inside the heat transfer shaft assembly; whereinheat is transferred away from the inner race of the bearing to theflywheel shaft, and from the flywheel shaft to the liquid heat transfermedium, and from the liquid heat transfer medium to the heat transfershaft assembly, and from the heat transfer shaft assembly to the coolingfluid.
 12. The method of claim 11, wherein the heat transfer shaftassembly comprises: a shaft extending from the enclosure and into thecavity; the shaft having an outer groove and an inner passage; a sleevedisposed about the shaft in spaced relation to the groove and in spacedrelation to an inner wall defining the cavity; a fluid channel jointlyformed by the sleeve and the groove, the fluid channel having thecooling fluid therein; wherein the closed fluid pathway extends throughthe fluid channel.
 13. The method of claim 12, wherein the groove ishelical.
 14. The method of claim 12, wherein, within the heat transfershaft assembly, the inner passage is downstream from the fluid channel.15. The method of claim 11: wherein the recirculating comprises: routingthe cooling fluid from the heat transfer shaft assembly to a reservoir;pumping the cooling fluid from the reservoir to the heat transfer shaftassembly; wherein the cooling the cooling fluid comprises cooling thecooling fluid via a heat exchanger.
 16. The method of claim 11, whereinthe dissipating heat comprises: transferring heat from the inner race tothe flywheel shaft using solid conduction; transferring heat from theflywheel shaft to the heat transfer shaft assembly via the liquid heattransfer medium liquid using conduction and convection.
 17. A gyroscopicroll stabilizer for a boat, the gyroscopic roll stabilizer comprising:an enclosure mounted to a gimbal for rotation about a gimbal axis andconfigured to maintain a below-ambient pressure; a flywheel assemblyincluding a flywheel and flywheel shaft; a first bearing for rotatablymounting the flywheel assembly inside the enclosure for rotation about aflywheel axis; the first bearing comprising an inner race and an outerrace, the inner race affixed to the flywheel shaft; a bearing blockdisposed between the outer race of the first bearing and the enclosureand configured to hold the outer race rotationally fixed relative to theenclosure; a motor operative to rotate the flywheel assembly; a bearingcooling circuit configured to transfer heat away from the outer race ofthe first bearing; the bearing cooling circuit having a closed fluidpathway for recirculating cooling fluid therein; wherein the closedfluid pathway includes a fluid channel disposed between the bearingblock and the enclosure and having the cooling fluid therein; whereinthe gyroscopic roll stabilizer is configured to transfer heat away fromthe outer race of the first bearing to the bearing block, and from thebearing block to the cooling fluid.
 18. The gyroscopic roll stabilizerof claim 17, wherein the bearing block comprises a groove facing theenclosure that defines at least a portion of the fluid channel.
 19. Thegyroscopic roll stabilizer of claim 18, wherein the groove peripherallysurrounds the flywheel axis.
 20. A method of operating a gyroscopic rollstabilizer for a boat, the method comprising: maintaining a belowambient pressure within an enclosure surrounding a flywheel assembly,the flywheel assembly including a flywheel shaft and a spinningflywheel; supporting the spinning flywheel for rotation about a flywheelaxis via a bearing, the bearing comprising an inner race and an outerrace, the inner race affixed to the flywheel shaft; supporting the outerrace via a bearing block disposed between the outer race and theenclosure and configured to hold the outer race rotationally fixedrelative to the enclosure; dissipating heat from the outer race bytransferring the heat by conduction and convection to a cooling fluidflowing through a fluid channel disposed between the bearing block andthe enclosure; cooling the cooling fluid by removing heat from thecooling fluid external to a portion of the enclosure maintained at thebelow-ambient pressure; and recirculating the cooling fluid through aclosed fluid pathway that includes the fluid channel.